1. Field of the Invention
The present invention relates to a process for patterning a nanocarbon material, a semiconductor device including a patterned nanocarbon material, and a method for manufacturing such a semiconductor device.
2. Description of the Related Art
Since H. W. Kroto, R. E. Smalley, and R. F. Curl discovered soccer ball-shaped molecules, called fullerenes, consisting of 60 carbon atoms in 1985 and S. Iijima discovered tubular structures, called carbon nanotubes, including rolled graphene sheets in 1991, various applications of these materials have been actively investigated.
The carbon nanotubes have excellent field emission properties, high heat conductivity, low weight, and high density; intercalate or deintercalate lithium ions due to electrochemical reaction; act as conductors or semiconductors depending on their chirality; and provide high-density currents. Therefore, carbon nanotubes have been investigated for applications in electrodes for display devices such as field emission displays (FEDs), applications in electrodes for lithium secondary batteries, applications in semiconductor devices such as field effect transistors, and applications in mechanical components.
In order to form channel layers or wiring layers containing the carbon nanotubes to manufacture semiconductor devices such as FETs, the following procedure is usually used to form carbon nanotube patterns: (i) a procedure including a step of forming a catalyst layer containing a transition metal element for selectively growing carbon nanotubes on a wafer to pattern the catalyst layer and a step of forming a carbon nanotube layer on the resulting catalyst layer by a chemical vapor deposition (CVD) process such as a plasma-enhanced CVD process or a thermal CVD process using a source gas containing hydrocarbon or (ii) a procedure including a step of forming negative patterns on a wafer using a photoresist material, a step of forming a carbon nanotube layer over the negative patterns and the wafer, and a step of removing the negative patterns and portions of the carbon nanotube layer that lie on the negative patterns by a lift-off process.
Procedure (i) has problems in that conditions for selectively growing the carbon nanotubes must be found, it is difficult to remove the catalyst layer on which the carbon nanotube layer is placed, and configurations of the devices are therefore limited. Procedure (ii) has a problem in that the temperature at which the carbon nanotube layer is formed must be lower than the heat-resistant temperature of the resist material.
Japanese Patent Laid-Open No. 2002-75960 discloses a technique for etching a carbonaceous material such as diamond-like carbon, carbon nanotube, fullerene, or graphite using a mask made of a material, resistant to oxygen plasma, containing an oxide such as silicon dioxide. For this technique, a process for forming the mask is, however, limited to a sputtering process or a CVD process using an organometallic compound. The technique therefore has a problem in that it is difficult to form an oxide layer for forming the mask without damaging a nanocarbon material and also has a problem in that such a nanocarbon material is deteriorated or damaged during the etching of the oxide layer. In particular, when the oxide layer is formed on the nanocarbon material by a sputtering process, the following problems occur: damages due to argon ions, the oxidation of the nanocarbon material, and the formation of a nonuniform oxide layer. When a silicon dioxide layer is formed by a CVD process using a compound such as tetraethoxysilane, the layer usually contains carbon and uniform layer, resistant to oxygen plasma, is therefore difficult to form. Furthermore, when the mask is removed by a dry etching process using halogen plasma, insulating films containing halogen are usually formed on the nanocarbon material.
Accordingly, the following process has been demanded: a process for patterning a nanocarbon material without deteriorating or damaging the material. Such a process is useful in manufacturing high-performance devices such as field effect transistors (FETs) and FEDs containing a nanocarbon material such as carbon nanotubes.